1. Field of the invention
The present invention relates to a throw away tip, and more particularly to a throw away tip suitable for back-turning, wherein a throw away tip cuts deeply into a work material in depth setting and machines in a different direction from that of the depth setting mainly at a right angle to the direction of the depth setting.
2. Related art
In back-turning, a cutting tool fixed to a machine is subject to a heavy load due to its large contact area with the work material during depth setting and subsequent machining. Especially when a cutting tool cuts deeply in depth setting, the cutting tool's contact area with the work material becomes quite large during machining. Conventionally, brazed tools or solid tools have been used, if a work material is to be cut into deeply prior to machining, to avoid shifting tips on the fixture and other problems.
In brazed tools or solid tools, however, the changing of tips is either difficult or impossible. Further, these types of cutting tools can be provided with only one tip. These problems cause a heavier workload and higher costs.
Despite the above-identified problems that brazed tools and other types of cutting tools have, conventional throw away tips have rarely been used for back-turning because conventional throw away tips may shift on the fixture when receiving a heavy load. Furthermore, there is no proposed throw away tip suitable for the back-turning operation where the tip cuts deeply into work material in depth setting and consequently receives a heavy load.
The present applicant disclosed a throw away tip in Japan Published Unexamined Utility Model Application No. S62-172505. Its plane view is shown in FIG. 4. This related-art throw away tip is constructed approximately in the shape of a triangle as seen from above. The related-art throw away tip is not suitable for cutting deeply (8 mm for instance) into work material in the depth setting and in machining the work material due to the following problems arising from its approximately triangular shape.
The related-art throw away tip must have a longer side which forms a major cutting edge 30 in order to perform back-turning in which the tip cuts deeply into the work material and then machines the work material. However, if the side forming the major cutting edge 30 is made longer, other sides must also be made longer, thus making the whole tip extremely large. Consequently, the resistance produced during the depth setting, along with other resistances, will increase, hindering the back-turning operation. Moreover, such a large tip will not be able to perform fine back-turning.
On the other hand, if the length of the major cutting edge 30 is made shorter(for instance 1-2 mm), cutting efficiency will be reduced because repeated operations of the depth setting and machining will be required to achieve sufficient depth of cut.
Some machines cut to a predetermined depth in one depth setting operation prior to machining. This type of machine will not be able to use the throw away tip shown in FIG. 4 if the major cutting edge is designed shorter.